A memory that is arranged in a line interface unit (LIU) has an error detection circuit that detects an error using an error correcting code (ECC), a parity, a frame check sequence (FCS), or the like. The LIU uses the error detection circuit to detect an error of data in the memory when receiving a packet.
The reliability of a recent transmitting device is improved by causing the LIU to be made redundant and thereby inhibiting communication from being stopped even if a failure occurs in the LIU. When the LIU is made redundant, a user packet or the like is input to the error detection circuit of the operating LIU, and the operating LIU may detect an error of data in the memory. On the other hand, the user packet or the like is not input to an error detection circuit of a standby LIU, and it is difficult for the standby LIU to detect an error of data in a memory.
Thus, even if an abnormality occurs in the memory of the standby LIU, the error of data in the memory is not detected until the transmitting device switches the operating LIU to a standby state. The error of data in the memory is detected when the operating LIU is switched from an operating state to the standby state. In addition, the standby LIU may not be used. Thus, a method is known, which is to detect an error of data in the memory by causing the operating LIU and the standby LIU to generate monitoring packets that are different from the user packet, and distributing the generated monitoring packets in the LIUs.
Specifically, the LIUs generate the monitoring packets having the highest priority set thereto so as to inhibit the generated monitoring packets from being discarded during the distributions. Subsequently, the LIUs execute reading or writing from or in the memories and distribute the generated monitoring packets. Then, the LIUs use the error detection circuits to detect an error of data in the memories when executing the reading or writing. Entries that are included in the memories and from or in which data is read or written vary depending on the type of the packet.
As related art, Japanese Laid-open Patent Publications Nos. 63-284941, 2005-269507 and the like have been disclosed.